1. Field of the Invention
The present invention generally relates to the fabrication of integrated circuits on substrates and to a method for reducing oxygen diffusion into dielectric layers.
2. Background of the Related Art
Consistent and fairly predictable improvement in integrated circuit design and fabrication has been observed in the last decade. One key to successful improvements is the multilevel interconnect technology that provides the conductive paths in an integrated circuit (IC) device. The shrinking dimensions of conductive or semi-conductive substrate features such as horizontal lines and vertical contacts, vias, or interconnects, in very large scale integration (VLSI) and ultra large scale integration (ULSI) technology, has increased the importance of improving the current density of semi-conductor devices.
In order to further improve the current density of semiconductor devices on integrated circuits, it has become necessary to use conductive materials having low resistivity and low dielectric constant (low k) materials (defined herein as having dielectric constants, k, less than about 3.0 for dielectric layers and less than about 5.5 for etch stops and barrier layers) as insulating layers to reduce the capacitive coupling between adjacent interconnects. Current dielectric material have relatively capacitive coupling between interconnects, which may lead to cross talk and/or resistance-capacitance (RC) delay, i.e., the time required to dissipate stored energy, that degrades the overall performance of semi-conductor devices.
However, typical low k dielectric materials are generally porous and require a barrier layer to prevent interlayer diffusion of materials into the low k dielectric materials. Conventional barrier layer materials typically have dielectric constants that are greater than 7.0, such as silicon nitride. When the conventional barrier layer materials are used in conjunction with low k dielectric materials, the resulting insulator stack typically minimizes the improved dielectric constant of the low k material effect and often produces a stack having a dielectric constant that is not much below 6.0.
One additional difficulty in using traditional low k dielectric materials as insulating layers is the increase in the use of copper in integrated circuits. Copper (Cu) is becoming an interconnect material of choice because of copper""s low resistivity (1.7 xcexcxcexa9-cm) and high current carrying capacity. However, copper diffuses more readily into surrounding materials and can alter the electronic device characteristics of the adjacent layers and, for example, form a conductive path across the dielectric layers, thereby reducing the reliability of the overall circuit and may even result in device failure. This diffusion characteristic of copper, especially with regard to the new low k films which tend to be porous and susceptible to diffusion, increases the need for diffusion resistant barrier layers with low k characteristics.
Silicon carbide (SiC) layers have been recognized as potential candidates for use as low k barrier materials. In particular, as disclosed in U.S. patent application Ser. No. 09/165,248, entitled xe2x80x9cA Silicon Carbide Deposition For Use As A Barrier Layer And An Etch Stopxe2x80x9d, filed Oct. 1, 1998, commonly owned by the assignee of the present application and incorporated by reference herein to the extent not inconsistent with the invention, silicon carbide layers are recognized as low k barrier layers.
However, low k silicon carbide layers are porous and susceptible to oxygen diffusion into the layer, particularly the surface of the layer. Oxygen may react with the silicon material in the silicon carbide layer to form oxides, which is believed to increases the diffusion of conducting materials, such as copper, into silicon carbide and reduce the overall effectiveness of the barrier layer. Oxygen diffusion into silicon carbide layers can occur by exposure to oxygen during deposition of the silicon carbide layer or during transport between processing chambers and cluster tools when the layers may be exposed to an oxidizing environment.
Additionally, oxygen incorporation in silicon carbide layers detrimentally affects bonding, or adhesion, of the layer to adjacent materials, especially to conducting metals such as copper, and may result in layer delamination of materials. Additionally, oxides formed in the silicon carbide layers typically have a lower density than the adjacent silicon-carbide material. The low density oxide formation in the surface and upper portions of a layer can result in the deformation of layers as bulges or xe2x80x9chumpsxe2x80x9d, which are particularly undesirable for conformally filling high aspect ratio features and may form voids and other deposition defects in subsequently deposited materials.
Therefore, there is a need for a process for reducing oxygen diffusion in low k layers. Ideally, the process would reduce oxygen content in barrier layers, such as silicon carbide layers used in copper metallization.
Aspects of the invention generally relate to a method for producing low dielectric constant layers, such as silicon carbide, that are resistant to oxygen diffusion and have low oxygen content, which may be useful as passivating and/or barrier layers in copper metallization. In one aspect of the invention, a method is provided for processing a substrate comprising depositing a low dielectric constant layer on a substrate in a processing chamber, introducing a processing gas into the chamber, generating a plasma of the processing gas, and exposing the low dielectric constant layer to the plasma of the processing gas.
In another aspect of the invention, a method is provided for processing a substrate, comprising depositing a silicon carbide layer on the substrate in a processing chamber, introducing a processing gas selected from the group of an inert gas, a nitrating gas, and combinations thereof, into the processing chamber, generating a plasma of the processing gas, and modifying a surface of the silicon carbide layer by exposing the silicon carbide layer to the plasma of the processing gas to form a passivating surface on the silicon carbide layer. The inert gas may comprise helium, argon, and combinations thereof, and the nitrating gas may comprise ammonia, nitrogen, a nitrogen and hydrogen mixture, nitrous oxide, and combinations thereof.
In another aspect, the invention provides a method for forming a low dielectric constant barrier layer on a substrate comprising depositing a low dielectric constant layer on the substrate, and then depositing a thin passivating layer on the low dielectric constant layer. The passivating layer comprises a silicon and nitrogen containing material such as silicon nitride or silicon oxynitride.